Fission yeast is a model organism for study of the molecular biology of cell cycle control. A gene of particular signifcance in controlling the rate of progression through both the G1 and G2 phases of the cell cycle (cdc2+) has previously been identified genetically. DNA sequences analysis and site-specific mutagenesis of the gene strongly suggest that it encodes a protein kinase. This proposal is concerned with three aspects of the molecular biology of cdc2+. (1) Since all known protein kinases are themselves phosphorylated and since genetic evidence suggests that the activity of the cdc2+ product is modulated during the cell cycle, the modification of the cdc2+ product by phosphorylation will be investigated. The possibility that the modification of the cdc2+ product might vary during the cell cycle will be particularly investigated. (2) The probable protein kinase activity of the cdc2+ product from yeast and after over-expression in E. coli will be investigated. (3) Targets of cdc2+ protein kinase phosphorylation will be sought. This will involve direct biochemical experiments, study of phosphoprotein changes during the cell cycle, analysed by 2-D gel electrophoresis and also classical genetics and analysis of cdc2(ts) suppressors. This proposal concentrates almost entirely on the cdc2+ gene product in the belief that it is of particular significance in the control of the cell cycle and that understanding its biochemical activity would open many new areas of cell cycle research.